Conventionally, evolution of a radio access method and a radio network of a cellular mobile communication (hereinafter, referred to as “Long Term Evolution (LTE)” or “Evolved Universal Terrestrial Radio Access (EUTRA)”), and a radio access method and radio network which realize higher-speed data communication through the use of a frequency band wider than the LTE (hereinafter, referred to as “Long Term Evolution-Advanced (LTE-A)” or “Advanced Evolved Universal Terrestrial Radio Access (A-EUTRA)”) have been examined in the 3rd Generation Partnership Project (3GPP).
In the LTE-A, it is requested that the LTE-A has backward compatibility with the LTE, that is, a base station apparatus of the LTE-A is made to be able to perform radio communication simultaneously with mobile station apparatuses of both the LTE-A and the LTE, and a mobile station apparatus of the LTE-A is made to be able to perform radio communication with base station apparatuses of both LTE-A and the LTE, and it has been examined that the LTE-A uses the same channel structure as the LTE. For example, in the LTE-A, a technology in which a plurality of Component Carriers (CCs) being frequency bands having the same channel structure as the LTE is used as one frequency band (wide-band frequency band) (frequency band aggregation; referred to also as Spectrum aggregation, Carrier aggregation, Frequency aggregation, or the like), has been proposed (Non-patent document 1).
Furthermore, in the LTE-A, other than a reference signal for channel estimation transmitted at a periodic timing set by a base station apparatus, a reference signal for channel estimation transmitted only when abase station apparatus provides notification of a transmission request has been proposed (Non-patent document 2).